Polyethylene compositions and resins are utilized in various applications and articles, for example, in the production of molded articles, blown films, and various other articles. Additives used for increasing the rate of nucleation during crystallization of semi-crystalline polymers are termed nucleators or nucleating agents. The addition of nucleating agents typically increases the overall rate of crystallization, and crystallization temperature of the polymers. This generally translates to faster solidification, and may be used to reduce the cycle time in processes like injection molding. Nucleators may also influence other properties, such as stiffness, toughness, haze, gloss, permeability and shrinkage. Nucleators that improve optical properties like haze and clarity are termed clarifiers. Various organic and/or inorganic additives may serve as nucleators, such as benzoic acids, talc, pigments, sorbitols, phosphate ester derivatives, and other polymeric species.
Derivatives of dibenzylidene sorbitol are well known clarifiers for polypropylene resins and films. The use of clarifiers in polyethylene resins and films is not common, due to much higher rates of crystallization in polyethylene compared to polypropylene, which makes haze reduction and the improvement of optical properties more challenging for polyethylene films and resins. Regarding the use of clarifiers, there is no known correlation between effective haze reduction for polypropylene compositions and effective haze reduction for polyethylene compositions.
Accordingly, there may be a continual need for nucleating agents which increase the rate of crystallization in polyethylene compositions while also reducing the haze and thereby improve the optical properties.